Kyra Harper

Sarah repels a potentially lethal Topside menace as she fights to locate a disappeared Helena, and the threat of Castor looms anew.

Leda and Castor are both on the hunt for original clone DNA, while a shocking revelation about their connection leaves the sisters reeling.

Castor pursues the Leda clones for original tissue samples; Helena, who's pregnant and imprisoned, is examined by a mysterious new villain.

Sarah and Art struggle to protect Helena behind enemy lines and end the siege.

Mark is taken down in a Prolethean shoot-out and Sarah must step in to help. Alison and Donnie come face-to-face with Jason Kellerman.

When Rachel makes a promise to Sarah, it comes with a hefty price; Coady and Benchman scheme to track down the Castor Original.